The present invention is directed to a tempo generating device for an electrical musical instrument, such as an electronic organ. In playing the organ, the organist desires to control the tempo at which automatic accompaniment and rhythm devices which have become commonplace in electronic organs provided an audio output. A standard type of rhythm unit provides a plurality of different audio output signals or voices such as bass drums, cymbals or others which are selectable by the player. The output signals of the rhythm unit occur in a predetermined and repeated pattern such as a waltz or others also selectable by the player. The tempo of the rhythm unit is the frequency or time interval at which the predetermined pattern is repeated.
In a previously used device, the instrument player selects a desired tempo by controlling a variable resistor circuit. By changing the resistance value of this circuit, the voltage level of its output signal varies and is used to adjust the frequency output of a voltage controlled oscillator. The output of the oscillator provides a tempo signal to control the repetition rate of the rhythm unit. In this type of device, the player estimates the tempo output based upon the position of a variable resistor knob or lever. No time relationship or correlation exists between the desired tempo and the movement of the indication knob of the variable resistor. The player has to listen to the audio signal being produced by the rhythm unit and thereafter adjusts the variable resistor until the desired tempo is achieved. Such a device is cumbersome to regulate and disturbing to an audience or other musicians in the surrounding area. Furthermore, the selection of an appropriate new tempo during play is particularly difficult.
An improvement over the variable resistor tempo device is the touch responsive device described in United States patent application for a Tempo Setting Device For An Automatic Rhythm Instrument, Ser. No. 585,403 by Masashi Shibahara. To select a desired tempo, the instrument player taps a touch plate a predetermined number of times at the desired tempo. The time interval between two predetermined and consecutive taps produces an analog voltage level at a magnitude related to the time interval. The analog voltage signal is applied as the input control signal to a voltage controlled oscillator. The oscillator provides a tempo output signal at an inerval related to the magnitude of the input analog signal in the same manner described with respect to the variable resistor tempo setting device. This touch responsive device establishes a positive time link or connection between the instrument player's desired tempo and the setting device. However, the voltage controlled oscillator is still necessary to produce a tempo signal in response to the variable level analog voltage signal in the same manner as in the variable resistance devices.
The present invention overcomes the difficulties and disadvantages of the known tempo setting devices by providing a digital device in which the instrument player selects a desired tempo by repetitively tapping a touch plate a predetermined number of times. Each tap by the player produces a touch pulse signal which controls the operation or mode of subsequent logic circuitry. In one mode, a digital value corresponding to the time interval between predetermined repetitive taps is stored in a digital circuit having a memory under control of a timing signal from a clock circuit. In a second mode, the stored digital value is read-out from the memory circuit under the control of a timing signal from the clock circuit. A tempo generator circuit is responsive to the completion of the read-out cycle and produces a tempo pulse output signal. The tempo generator circuit also provides a reset signal to the memory circuit to repeat the read-out cycle. The output pulses from the tempo generator are spaced apart as a function of the time interval between the predetermined repetitive taps by the instrument player.